The common edible mussel, Mytihis, attached to rock 

 by fine but strong secreted threads. ( England. Ralph 

 Buchsbaum ) 



sand is mixed with mud and provides a firmer cover- 

 ing, burrowing clams of many other kinds live in con- 

 stant readiness to jerk back into the buried shell. 

 Only when undisturbed do they extend above the 

 mud the siphon or "neck," which is actually part of 

 the posterior end of the mantle, a part through which 

 water and food enter and then water and wastes are 

 discharged. 



This is the way of life of the economically impor- 

 tant soft-shell clam Mya arenarici, whose brittle, thin, 

 oval shell averages less than 5 inches in length and 

 bears a large spoon-shaped projection on the left 

 valve at the hinge. The soft-shell is common on both 

 coasts of America, having been introduced acciden- 

 tally on Pacific shores along with Atlantic oysters. 

 Mya is a favorite for New England chowders and 

 clambakes. In the Arctic it is the principal diet of the 

 walrus, which uses its tusks as a clam rake to dig 

 the shellfish from the bottom. 



An extremely popular clam with the same burrow- 



ing habits is the quahog Venus nienenaria, known 

 also as the hard-shell clam, the little-neck clam, and 

 the round clam. Immature ones, less than 3 inches 

 in length, are called cherrystone clams. This is the 

 shell from which New England Indians cut and 

 pierced small beads as shell money (wampum) that 

 could be carried as a necklace string. 



West Coast Indians showed a preference for the 

 bent-nosed clam Maconui nasuta. which lies upon its 

 left side several inches below the beach surface 

 and extends to the water above a long, slender, in- 

 current siphon. The excurrent siphon is a separate 

 tube, equally slender but somewhat shorter, dis- 

 charging into the sand near the clam. The asym- 

 metrical bend in the incurrent siphon matches the up- 

 ward bend of the bent-nosed clam's shell. Usually the 

 incurrent siphon extends as much as three-quarters of 

 an inch above the mud. It waves back and forth, 

 turned downward and sucking in food particles from 

 the surface sediments. At intervals of two to three 

 minutes the clam retracts its siphon slightly and 

 flushes out any inedible or coarse materials. At longer 

 intervals it pulls the siphon well down into the mud 

 and then extends it to the surface a few inches away, 

 to sample a new feeding area. 



The largest burrowing clam in the world is the 

 edible geoduck [pronounced goo'ee-duck] of Puget 

 Sound and adjacent coasts of British Columbia, 

 Washington, Oregon, and northern California. Pa- 

 nope generosa may weigh as much as twelve pounds, 

 but the 8-inch shell accounts for only a minor part of 

 this. The shell is relatively thin and in a mature geo- 

 duck fails to cover the body. The siphons are almost 

 as large as the body proper and stretch far enough 

 to allow the clam to live three or four feet below the 

 surface of the muddy bottom. 



Geoducks constitute a sports fishery in Washing- 

 ton, with a bag limit of three per day enforced by 

 wardens. Almost as strict protection comes from the 

 animals' position in the beach. They are exposed only 

 by tides lower than mean low (minus tides), and 

 consequently are within reach of a man with a shovel 

 for only a few hours a month. 



Apparently it is only a small step from maintain- 

 ing a vertical burrow in firm mud to boring into soft 

 rock. The arctic rock-borer Saxicava, with a 1- to 

 I'.'i-inch shell, holds tight with its foot while using 

 the anterior end of the shell as a scraping tool with 

 which to cut cylindrical cavities as much as six inches 

 deep into rock and concrete. A later inhabitant of the 

 same burrow in a breakwater or seawall may not be 

 satisfied with the cavity, and may enlarge it or intro- 

 duce a side branch. After a while the whole man- 

 made structure is weakened and may crumble. The 

 larger piddocks (Zirfciea and Martesia) show simi- 

 lar habits, using their 4-inch shells to bore into wharf 

 pilings with disastrous results. 



190 i 



